[s-cars] Troubleshoot a no start issue (Brooke Fairbanks)

[Paul Heneghan]

Hello Brooke,

Commiserations on your plight.  It's not much consolation I'm afraid, but
congratulations on becoming one of the world's leading authorities on the
'AAN no start condition'!

I can't really add anything new, but just stating things with a different
slant might help, so here is my two pennies' worth:

You need a spark, fuel and compression.

1a. You've seen a spark at one plug.  Check that you get a spark at the
other plugs as well.
1b. Are the sparks feeble?  It's worth getting hold of one of those cheap
testers that can vary the spark gap to see if they can all jump a few mm in
air (I think it's something like 3,000V/mm).  It's much more difficult to
produce a spark when you have an air/fuel mix under a few bar pressure, so
you want a big fat spark in air.
1c. Are the spark plugs in good condition?  Replace if suspect.
1d. Is the spark happening at the right time?  This is much more difficult
to check.  For starters, check the mechanical synchronisation (again) - the
timing marks on cam, crank pulley and particularly the flywheel.  There is
past history for I5 engines to shear the key in the crank pulley which can
cause the crank/cam relationship to shift back and forth a few degrees.  If
the marks on the flywheel and crank pulley always line up, then you can
probably rule that out.  Don't be fooled by extra false marks on cam pulley,
crank pulley and flywheel.  Many of us have wasted an hour or two in the
past because of that.  Use a dial indicator down a spark plug hole to
determine where TDC is if you are unsure of the validity of any of the
marks.
1d. Next check the electronic synchronisation.  How are you at electrical
diagnosis and faultfinding? The AAN is famous for being fussy about refusing
to produce a spark if certain events are outside of a timing window.  Look
at the article on diagnosing a no-start condition on an S2:
http://www.picotech.com/auto/tutorials/audi.html.  Ignore the few factual
errors at the beginning (B3 instead of 3B, 270hp instead of 220hp, etc.) -
it's a good description of faultfinding a spark problem on a Motronic engine
(which turns out to be a mechanical problem).
Read Scot Mockry's article on Audi turbo no-start conditions:
http://www.sjmautotechnik.com/trouble_shooting/nostart.html
Read the sections of the website that discuss the way that the various
hall-effect sensors contribute to the timing information received by the
ECU.
http://www.sjmautotechnik.com/trouble_shooting/20vtime.html
http://www.sjmautotechnik.com/trouble_shooting/20vhall.html
Get an oscilloscope and check that those signals are present on the
terminals of the sensors, and check that they also appear on the pins of the
ECU - that eliminates wiring problems.  Check all your grounds are really at
ground potential - poor grounding can cause some really confusing symptoms.
Check that the ECU produces sensible outputs to the POSs on all five
channels.  Use the Reference Sensor as the trigger for all the timing tests.
You know that this signal is always 62 degrees BTDC for cylinder #1.
2a. Fuel.  I know very little about this as I have yet to have my first
fuel-related problem on an AAN.  I'd probably try something like putting all
the injectors into measuring test tubes and checking delivery quantities and
spray patterns - is that possible on the AAN with injectors plugged into the
fixed fuel rail?
2b. Can you test the delivery rate of the FI pump, and the fuel pressure?
2c. Is there an Output Test you can execute from VAG-COM that pulses on the
injectors and the WGFV?
2d. Clogged Cat?
2e. Clogged fuel filter?
2f. Some restriction in the air intake?  Clogged filter?  Hose come off or
split?
2g. Turbo/bypass/wastegate/frequency valve problems?  (I'm grasping at
straws here!).
2h. Check for vacuum leaks.  Use a cheap vacuum tester - should show lots of
vacuum when cranking the engine with the throttle closed.
2i. Have you confiscated your neighbour's son's football, and in retaliation
has he put sugar in your fuel, a couple of potatoes up your exhaust pipe,
and a slit in your Michelin Man hosepipe?
2j. Immobiliser problem?  How does the immobiliser work in these cars?  Does
it refuse to turn over, refuse to produce a spark, or refuse to provide fuel
to the injectors?
3. Compression.  I think you've already ruled that out.

Keep us updated.

Paul